Methods for the fractionation and analysis of proteins are developed and applied to the purification of specific proteins for the study of their function and structure. Ion-exchange displacement (IED) chromatography is being developed for the fractionation of macromolecules and particles of biological interest, employing polyanions differing in number of charges per molecule as displacers. The procedure is particularly advantageous when large amounts of source material must be used to obtain sufficient amount of a minor component, since the resolving power of the system can be focused on the narrow range of affinity represented by the protein of interest and its nearest neighbors. However, it is also applicable to ion-exchange HPLC. Recent efforts have been directed toward the simplification of the preparation of narrow-range displacers. Application of the method to the isolation of the myeloblast maturation factor (MMF) of W. Evans from guinea pig serum has provided an electrophorectically homogenous protein after two stages of displacement chromatography, but its chromatographic fractions were not uniform with respect to specific activity of MMF. An explorarion of the binding of serum proteins to several metal chelate and hydrophobic absorbents suggests that chromatography on some of these before IED-chromatography will simplify and improve the purification.